Communication using a 60 GHz carrier is being proposed for implementation in higher data rate systems. Standardization efforts are emerging in entities such as the Institute of Electrical and Electronics Engineers (IEEE) 802.15.3c standard and in European Computer Manufacturers Association (ECMA) standards. In ECMA, single carrier (SC) is the method of choice for simple devices operating in the 60 GHz band. In IEEE 802.15.3c, several optional physical layer methods have been accepted, one of them is SC and another is OFDM.
Multipath channels require equalization for reducing the inter-symbol interference (ISI) effect. In SC systems, channel equalization is typically done using a decision feedback equalizer (DFE) that includes a feed-forward part using a linear filter as a feed-forward equalizer (FFE) followed by a decision feedback section. Feed-forward equalizers may be implemented either in the time domain or in the frequency domain. In the time domain, this is typically done by a linear filter operating at the sampling frequency. Such an arrangement may require assignment of multipliers proportional to the delay spread of the channel. In contrast, a frequency domain equalizer (FDE) may perform a fast Fourier transform (FFT), correct the gains in the frequency domain, and then perform inverse FFT back to the time domain. Such an arrangement is capable of handling various types of multipath channels and for medium-to-long delay spread sizes the complexity is smaller compared to time domain FFEs.
Frequency domain equalizers appear to be included as part of the proposals in IEEE 802.15.3c. However, the FFT may require that the channel will circularly affect the transmitted signal such as commonly utilized in OFDM systems, for example, where a cyclic prefix may be attached to the transmitted symbol. FDEs for single carrier systems may also use a proper prefix for creating this circular effect, and there are two methods for doing so. One is by utilizing a regular cyclic prefix wherein the contents of the suffix are also attached as a prefix. Another is by utilizing a predetermined sequence which may be attached between every two blocks. By keeping the size of the block with a predetermined sequence, including the prefix, as a power of 2, FFT treatment may be implemented. When a regular cyclic prefix is considered, the block size exclusive of the prefix may have a length that is a power of two.
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